1. Technical Field
The present invention relates generally to the art of electrolytic cells, and particularly to an expandable electrode for such cells. The present invention will be described with reference to an expandable anode for an electrolytic cell, although it will be apparent to those skilled in the art that the principles of the present invention are also applicable to the construction of an expandable cathode.
2. Description of the Prior Art
The use of expandable electrodes is well known in chlorine and caustic producing electrolytic cells. In such cells, the electrolyte has a high electrical resistance. For this reason, the gap between the anode and the adjacent cathode should be as small as possible. Cathodes in commercial electrolytic cells are typically very large. A cathode may have an overall height of about two feet. The cathode, which can as an example be a steel screen, may become misshapen and distorted through use and with age. This presents an irregular surface. The cathode can be out, from top to bottom, as much as one half inch. Also, the thickness of a coating on the cathode can vary. This has, in the past, prevented placing the cathode and anode close together, for instance, less than about one-half inch apart.
U.S. Pat. No. 3,674,676 discloses an anode assembly which comprises at least two opposed working faces on opposite sides of an anode riser. Supporting expandable or contractible springs connect the anode working faces, both mechanically and electrically, to the anode riser and hold the working faces spaced away from the riser. During assembly of an electrolytic cell, or replacement of an anode assembly, the anode assembly is contracted so that the anode working faces are relatively close to the anode riser. When the anode assembly is inserted into a cell, a working face may be on the order of about one-half inch from an adjacent cathode. After insertion of the anode assembly into a cell, the assembly is caused or allowed to expand, substantially reducing the gap between an anode working face and an adjacent cathode. The anode assembly of U.S. Pat. No. 3,674,676, is often referred to as a "minimum-gap" anode.
The '676 patent, in an embodiment, discloses an expandable anode assembly in which each anode working face is present in two sections separated by a gap. Thus the anode comprises four working faces, two on each side of the riser. Each face is connected to the riser by a single spring arm. The spring arm is connected to each face through a series of aligned resistance welds. This maintains each face generally parallel with the anode riser, at least along the weld line. However, pressure on an anode face at a point removed from the line of resistance welds, caused for instance by an extreme curvature in the cathode, can force the anode face to rotate. This will create a variable gap between the anode face and the cathode, resulting in a poor current distribution across the anode face, and overloading of an area or areas of the face.
U.S. Pat. No. 4,033,849 also discloses a "minimum-gap" anode assembly. The anode assembly comprises spring connectors between the riser and the anode working faces. Each anode working face is connected to the riser by two connectors which extend outwardly from the riser. The connectors are thus attached to an anode working face at spaced apart locations on opposite sides of the riser. The connectors have a bent configuration and are under compression. The tendency of each connector is to expand from its bent configuration. This maintains each anode working face, in the space between the points of attachment of the connectors to the anode working face, under tension, which in turn keeps the working faces generally planar. The component parts are dimensioned so that each anode working face is under tension when the anode is in an expanded state, as well as in a contracted state.
U.S. Pat. Nos. 4,129,292 and 4,231,143 disclose subject matters related to that of U.S. Pat. No. 4,033,849.
U.S. Pat. No. 4,154,667 discloses a method for converting a conventional box-type anode of an older chlorine or caustic electrolytic cell to an expandable "minimum-gap" anode.
Other patents showing related prior art are U.S. Pat. Nos. 4,120,773; 4,096,054; and 4,028,214.